Africa is the setting for the long dawn of human history. From about four million years ago ape-like creatures walk upright on two feet in this continent. Intermediate between apes and men, they have been named Australopithecus. Later, some two million years ago, the first creatures to be classed as part of the human species evolve in Africa. They develop a technology based on sharp tools of flint, introducing what has become known as the Stone Age.

About a million years ago humans explore northwards out of Africa, beginning the process by which mankind has colonized the planet.

Out of Africa: more than a million years ago

Homo erectus is the variety of human who moves out of the continent of Africa, to spread through much of Asia and Europe. This move from Africa is usually dated to about a million years ago, but this may be too recent. First reports of two skulls found in 1999 at Dmanisi, in South Georgia, describe them as 1.8 million years old.

Fossil remains of this kind have been found as far afield as Java in southeast Asia (the first to be discovered, in 1891), Beijing in northern China, and within Europe in Greece, Germany and England - in addition to numerous sites in Africa. The European skulls differ from the Asian in various ways (larger brains, smaller teeth), causing some anthropologists to classify them not as Homo erectus but as an archaic version of our own species, Homo sapiens.

The spread of our species: from 60,000 years ago

After Homo erectus has spread through the linked central land mass of our planet (Africa and Eurasia), he is succeeded within that region by varieties of Homo sapiens - the Neanderthals and then modern humans. It is modern humans who take the next step in colonizing the habitable earth.

The dates are still uncertain and much disputed. But at some time after 60,000 years ago people cross from southeast Asia to Borneo, the Philippines, New Guinea and Australia. And at some time after 30,000 years ago humans make the short but difficult leap from northeast Asia to northwest America.

Temporary bridges: 60,000 - 10,000 years ago

The Ice Ages play an essential part in mankind's advance from Asia into both Australia and America. The effect of an ice age is to lower the sea level by 100 metres and more. This narrows the gaps between many islands and sometimes even exposes a complete land ridge.

One such sunken ridge is the Sahul Shelf, under the largest stretch of sea between the Indonesian islands and Australia. Another lies between Siberia and Alaska.

The first Australians: from 60,000 years ago

The islands of Indonesia are like a string of beads pointing towards Australia. Stone Age hunter-gatherers no doubt find much of their food on the shores and in the shallows, and soon use rafts to reach offshore reefs. Probably the first people to arrive on slightly more distant islands have been carried there by accident rather than intention.

But there is a plentiful supply of food wherever they make landfall. With an ice age reducing the level of the Timor Sea (see Ice Ages), this series of hops for mankind sooner or later reaches Australia. The earliest traces of human habitation in the continent are now tentatively dated between 60,000 and 50,000 years ago.

The first Americans: 30,000 - 5000 years ago

During the most recent of the Ice Ages, lasting from 30,000 to 10,000 years ago, an undersea ridge between Siberia and Alaska emerges from the sea. Known as the Bering Land Bridge, it lies partly south of the ice cap. It develops a steppe-like ecology of grasslands, grazed by large animals such as horses, reindeer and even mammoth.

Gradually, in many separate incursions, the hunter-gatherers of the Siberian steppes pursue their prey across the land bridge and into America. When the melting ice submerges the bridge, about 10,000 years ago, these northeast Asians become isolated as the aboriginal Americans.